1. Field of the Invention
The present invention relates to a polyester resin composition and a method of producing the same, a polyester film, and a solar cell power generation module.
2. Description of the Related Art
Polyester resin is widely used in various fields because of the mechanical properties, heat resistance, and electrical properties thereof. For instance, a film prepared by using polyester resin is applicable to outdoor uses such as a solar cell power generation module, a lighting film, or an agriculture sheet. In these application modes, the film is required to have a high weather resistance because it is placed in such an environment where it is constantly exposed to wind and rain.
Particularly in recent years, from the viewpoint of preserving the global environment, photovoltaic power generation converting sunlight into electricity has drawn attention. A solar cell module used for the photovoltaic power generation has a structure including a (sealing material), solar cell devices, a sealing material, and a backsheet that are stacked in this order on a glass substrate through which sun light enters.
The solar cell power generation module is required to have a high weather-proof performance of securing cell performances such as power generation efficiency over a long period of time, several tens of years, even in a hard use environment where the module is exposed to wind and rain or direct sunlight. In order to impart such weather-proof performance, respective materials that compose the solar cell power generation module, including a backsheet and a sealing material that seals the devices, are also required to have weather resistance.
For the backsheet included in the solar cell power generation module, generally a resinous material such as polyester resin is used. Polyester tends to degrade with time because the terminal carboxy groups thereof work as a self-catalyst, causing easily hydrolysis in an environment where water exists. For this reason, a polyester resin that is used for the solar cell power generation module installed in such an environment as outdoors where it is exposed constantly to wind and rain is requested to suppress the hydrolysis property thereof.
A polyester resin that is used for outdoor applications other than the solar cell power generation module is also requested to suppress the hydrolysis property.
As a polymerization method of polyester resin, a polymerization method using an antimony catalyst has been mainly studied, but there is an attempt to use a titanium catalyst that is environmentally-compatible. Regarding a polyester resin composition prepared by using a titanium catalyst and a polyester resin film obtained from the composition, Japanese Patent Application Laid-Open (JP-A) No. 2007-204538 discloses providing a polyester film having improved environmental resistances such as hydrolysis resistance and weather resistance by using a titanium catalyst and a phosphorous compound and regulating the amount thereof. Further, JP-A No. 2004-19075 discloses a polyester resin composition and a film thereof, which are prepared by using a titanium catalyst and a phosphorus compound and are reduced in foreign substances derived from the catalyst. A heat resisting polyester film prepared by using a titanium catalyst and a phosphorus compound is disclosed in reference example 2 of Japanese Patent No. 3396995.
However, the problem is that the polyester films disclosed in JP-A Nos. 2007-204538 and 2004-19075 and Japanese Patent No. 3396995 are insufficient in hydrolysis resistance and productivity. Further, when the polyester films are used for the solar cell power generation module, there is also another problem of insufficient withstanding voltage.